Definitions for corundumkəˈrʌn dəm
Random House Webster's College Dictionary
a mineral, aluminum oxide, Al2O3, noted for its hardness: transparent varieties, as sapphire and ruby, are used as gems, other varieties as abrasives: often made synthetically.
Origin of corundum:
1720–30; < Tamil kuruntam; akin to Skt kuruvinda ruby
very hard mineral used as an abrasive
An extremely hard mineral, a form of aluminum oxide with the chemical formula AlO, that occurs in the form of the gemstones sapphire and ruby; it is used as an abrasive.
Origin: From குருந்தம்.
the earth alumina, as found native in a crystalline state, including sapphire, which is the fine blue variety; the oriental ruby, or red sapphire; the oriental amethyst, or purple sapphire; and adamantine spar, the hair-brown variety. It is the hardest substance found native, next to the diamond
Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. All other colors are called sapphire, e.g., "green sapphire" for a green specimen. The name "corundum" is derived from the Tamil word kuruntam meaning "ruby", and related to Sanskrit kuruvinda. Because of corundum's hardness, it can scratch almost every other mineral. It is commonly used as an abrasive, on everything from sandpaper to large machines used in machining metals, plastics, and wood. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average hardness near 8.0. In addition to its hardness, corundum is unusual for its density of 4.02 g/cm³, which is very high for a transparent mineral composed of the low atomic mass elements aluminium and oxygen.
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